MELANIN - A 2-EDGED-SWORD

Melanin is both photosensitizer and photoprotector. Skin cancer rates decrease with increasing constitutive pigmentation, yet the pigment ha s been shown to be photoreactive and capable of producing damaging rea ctive oxygen species. We utilized model systems of related cells or si milar cell type that vary in constitutive and in induced pigment. Indu ction of eumelanin in Cloudman S91 mouse melanoma cells leads to less UV-induced killing and to less mutation induction at the ouabain locus (Na+, K+-ATPase). Pigmented mouse melanocytes, melan-b (brown) and me lan-a (black) were slightly less sensitive than melcan-c (albino) mela nocytes to killing after UVC and UVA but were more sensitive to killin g after UVB and UVB + UVA. Pigment had a small sensitizing effect on p yrimidine dimer DNA damage in both the melanoma cells and the melanocy tes. The lack of consistency in these results suggests that intracellu lar pigment may disregulate the milieu interieur resulting in end effe cts that are unrelated to the original genomic damage.